691 research outputs found
The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-type galaxies
with the presence of optical morphological peculiarities, as measured by the
fine-structure index (Sigma). HI mapping observations from the literature are
used to track the cold-gas content, and archival ROSAT PSPC data are used to
quantify the hot-gas content. We find that E and S0 galaxies with a high
incidence of optical peculiarities are exclusively X-ray underluminous and,
therefore, deficient in hot gas. In contrast, more relaxed galaxies with little
or no signs of optical peculiarities span a wide range of X-ray luminosities.
That is, the X-ray excess anticorrelates with Sigma. There appears to be no
similar trend of cold-gas content with either fine-structure index or X-ray
content. The fact that only apparently relaxed E and S0 galaxies are strong
X-ray emitters is consistent with the hypothesis that after strong disturbances
such as a merger hot-gas halos build up over a time scale of several gigayears.
This is consistent with the expected mass loss from stars.Comment: 12 pages, latex, 5 figures. Accepted for publication in A
Effects of Cold Storage on Nondiapausing Eggs of the Western Corn Rootworm (Coleoptera: Chrysomelidae)
Western corn rootworm, Diabrotica virgifera virgifera LeConte, became much easier to research with the development of a nondiapausing rootworm strain. In the event that the eggs cannot be used immediately researchers have been known to delay egg hatch by storing the eggs at low temperatures. It is not well known how this technique could affect egg hatch or larval development, which could alter the results of an experiment. To test for this nondiapausing eggs of the western corn rootworm were stored at low temperatures to test for potential negative effects on hatch and larval development. Eggs were stored in either soil or agar and placed in refrigerators set to 4 or 8.5°C. Nondiapausing eggs were exposed to the cold for 1, 2, or 4 wk and then placed in a chamber set to 25°C. Eggs were then tested for average hatch percentage in Petri dishes and average larval recovery from containers with seedling corn. Results showed a significant reduction in percent hatch for eggs stored at 4°C for 4 wk. Larval recovery was significantly reduced in eggs stored for 4 wk at both 4 and 8.5°C. Within the treatments tested, egg storage for less than 4 wk in soil at 8.5°C provided the best hatch and larval recovery. Researchers wishing to store eggs may use these results to improve their rearing or testing of western corn rootworm
Star Clusters in the Tidal Tails of Interacting Galaxies: Cluster Populations Across a Variety of Tail Environments
We have searched for compact stellar structures within 17 tidal tails in 13
different interacting galaxies using F606W- and F814W- band images from the
Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). The
sample of tidal tails includes a diverse population of optical properties,
merging galaxy mass ratios, HI content, and ages. Combining our tail sample
with Knierman et al. (2003), we find evidence of star clusters formed in situ
with Mv < -8.5 and V-I < 2.0 in 10 of 23 tidal tails; we are able to identify
cluster candidates to Mv = -6.5 in the closest tails. Three tails offer clear
examples of "beads on a string" star formation morphology in V-I color maps.
Two tails present both tidal dwarf galaxy (TDG) candidates and cluster
candidates. Statistical diagnostics indicate that clusters in tidal tails may
be drawn from the same power-law luminosity functions (with logarithmic slopes
~ -2 - -2.5) found in quiescent spiral galaxies and the interiors of
interacting systems. We find that the tail regions with the largest number of
observable clusters are relatively young (< 250 Myr old) and bright (V < 24 mag
arcsec^(-2)), probably attributed to the strong bursts of star formation in
interacting systems soon after periapse. Otherwise, we find no statistical
difference between cluster-rich and cluster-poor tails in terms of many
observable characteristics, though this analysis suffers from complex,
unresolved gas dynamics and projection effects.Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 8
figure
The Infrared Properties of Hickson Compact Groups
Compact groups of galaxies provide a unique environment to study the
mechanisms by which star formation occurs amid continuous gravitational
encounters. We present 2MASS (JHK), Spitzer IRAC (3.5-8 micron) and MIPS (24
micron) observations of a sample of twelve Hickson Compact Groups (HCGs 2, 7,
16, 19, 22, 31, 42, 48, 59, 61, 62, and 90) that includes a total of 45
galaxies. The near-infrared colors of the sample galaxies are largely
consistent with being dominated by slightly reddened normal stellar
populations. Galaxies that have the most significant PAH and/or hot dust
emission (as inferred from excess 8 micron flux) also tend to have larger
amounts of extinction and/or K-band excess and stronger 24 micron emission, all
of which suggest ongoing star formation activity. We separate the twelve HCGs
in our sample into three types based on the ratio of the group HI mass to
dynamical mass. We find evidence that galaxies in the most gas-rich groups tend
to be the most actively star forming. Galaxies in the most gas-poor groups tend
to be tightly clustered around a narrow range in colors consistent with the
integrated light from a normal stellar population. We interpret these trends as
indicating that galaxies in gas-rich groups experience star formation and/or
nuclear actively until their neutral gas consumed, stripped, or ionized. The
galaxies in this sample exhibit a ``gap'' between gas-rich and gas-poor groups
in infrared color space that is sparsely populated and not seen in the Spitzer
First Look Survey sample. This gap may suggest a rapid evolution of galaxy
properties in response to dynamical effects. These results suggest that the
global properties of the groups and the local properties of the galaxies are
connected.Comment: 34 pages, 26 figures, accepted for publication in AJ, higher quality
images available in publicatio
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
The Association of Patient Factors, Digital Access, and Online Behavior on Sustained Patient Portal Use: A Prospective Cohort of Enrolled Users
BACKGROUND: As electronic health records and computerized workflows expand, there are unprecedented opportunities to digitally connect with patients using secure portals. To realize the value of patient portals, initial reach across populations will need to be demonstrated, as well as sustained usage over time.
OBJECTIVE: The study aim was to identify patient factors associated with short-term and long-term portal usage after patients registered to access all portal functions.
METHODS: We prospectively followed a cohort of patients at a large Department of Veterans Affairs (VA) health care facility who recently completed identity proofing to use the VA patient portal. Information collected at baseline encompassed patient factors potentially associated with portal usage, including: demographics, Internet access and use, health literacy, patient activation, and self-reported health conditions. The primary outcome was the frequency of portal log-ins during 6-month and 18-month time intervals after study enrollment.
RESULTS: A total of 270 study participants were followed prospectively. Almost all participants (260/268, 97.0%) reported going online, typically at home (248/268, 92.5%). At 6 months, 84.1% (227/270) of participants had visited the portal, with some variation in usage across demographic and health-related subgroups. There were no significant differences in portal log-ins by age, gender, education, marital status, race/ethnicity, distance to a VA facility, or patient activation measure. Significantly higher portal usage was seen among participants using high-speed broadband at home, greater self-reported ability using the Internet, and routinely going online. By 18 months, 91% participants had logged in to the portal, and no significant associations were found between usage and demographics, health status, or patient activation. When examining portal activity between 6 and 18 months, patients who were infrequent or high portal users remained in those categories, respectively.
CONCLUSIONS: Short-term and long-term portal usage was associated with having broadband at home, high self-rated ability when using the Internet, and overall online behavior. Digital inclusion, or ready access to the Internet and digital skills, appears to be a social determinant in patient exposure to portal services
The Antennae Galaxies (NGC 4038/4039) Revisited: ACS and NICMOS Observations of a Prototypical Merger
The ACS and NICMOS have been used to obtain new HST images of NGC 4038/4039
("The Antennae"). These new observations allow us to better differentiate
compact star clusters from individual stars, based on both size and color. We
use this ability to extend the cluster luminosity function by approximately two
magnitudes over our previous WFPC2 results, and find that it continues as a
single power law, dN/dL propto L^alpha with alpha=-2.13+/-0.07, down to the
observational limit of Mv~-7. Similarly, the mass function is a single power
law dN/dM propto M^beta with beta=-2.10+/-0.20 for clusters with ages t<3x10^8
yr, corresponding to lower mass limits that range from 10^4 to 10^5 Msun,
depending on the age range of the subsample. Hence the power law indices for
the luminosity and mass functions are essentially the same. The luminosity
function for intermediate-age clusters (i.e., ~100-300 Myr old objects found in
the loops, tails, and outer areas) shows no bend or turnover down to Mv~-6,
consistent with relaxation-driven cluster disruption models which predict the
turnover should not be observed until Mv~-4. An analysis of individual ~0.5-kpc
sized areas over diverse environments shows good agreement between values of
alpha and beta, similar to the results for the total population of clusters in
the system. Several of the areas studied show evidence for age gradients, with
somewhat older clusters appearing to have triggered the formation of younger
clusters. The area around Knot B is a particularly interesting example, with an
~10-50 Myr old cluster of estimated mass ~10^6 Msun having apparently triggered
the formation of several younger, more massive (up to 5x10^6 Msun) clusters
along a dust lane.Comment: 84 pages, 9 tables, 31 figures; ApJ accepte
Mammals from the Kanopolis Local Fauna, Pleistocene ( Yarmouth) of Ellsworth County, Kansas
11-44http://deepblue.lib.umich.edu/bitstream/2027.42/48492/2/ID343.pd
Merging Cold Fronts in the Galaxy Pair NGC 7619 and NGC 7626
We present results from {\it Chandra} observations of the galaxy pair NGC
7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray
images show a brightness edge associated with each galaxy, which we identify as
merger cold fronts. The edges are sharp, and the axes of symmetry of the edges
are roughly anti-parallel, suggesting that these galaxies are falling towards
one another in the plane of the sky. The detection of merger cold fronts
implies a merging subgroup scenario, since the alternative is that the galaxies
are falling into a pre-existing keV halo without a dominant galaxy of
its own, and such objects are not observed. We estimate the 3D velocities from
the cold fronts and show that the velocity vectors are indeed most likely close
to the plane of the sky, with a relative velocity of \sim1190\kms. The
relative velocity is consistent with what is expected from the infall of two
roughly equal mass subgroups whose total viral mass equals that of the Pegasus
group. We conclude that the Pegasus cluster is currently forming from a major
merger of two subgroups, dominated by NGC 7619 and NGC 7626. NGC 7626 contains
a strong radio source, a core with two symmetric jets and radio lobes. Although
we find no associated structure in the X-ray surface brightness map, the
temperature map reveals a clump of cool gas just outside the southern lobe,
presumably entrained by the lobe, and an extension of cooler gas into the lobe
itself. The jet axis is parallel with the projected direction of motion of NGC
7626 (inferred from the symmetry axis of the merger cold front), and the
southern leading jet is foreshortened as compared to the northern trailing one,
possibly due to the additional ram pressure the forward jet encounters.Comment: 11 pages, 9 figures. Accepted to ApJ. Minor changes to be consistent
with accepted versio
- …